To ensure that their products are of a high quality and free from any contamination introduced during the manufacturing process, companies in many industries, including the food preparation, electronics, medical device manufacturing and drug preparation industries, must manufacture their products in an unusually clean, sterile environment which is free of sources of contamination. Further, because the machinery used in production facilities is often very noisy, steps must be taken to maintain sound emissions at a tolerable level, i.e., a level which is comfortable for employees working in the facility and which allows the employees to easily communicate with each other. Regretably, those means which may be taken to control sound emissions lie at crosspurposes to conventional means for avoiding contamination.
In the past, acoustical panels have been used to control sound emissions but these panels are not suitable for use in an environment where sterile, clean conditions are required. Acoustical panels used in the past have generally been made of a fibrous material to which a paint or other film-forming material was applied for appearance purposes. Also, acoustical panels traditionally have had a roughened irregular surface which created both coating difficulties, as well as cleaning difficulties. As a result, it has been extremely difficult to provide appropriate control of sound emissions in those environments where sterile and clean conditions are required, such as in typical clean-room facilities. Accordingly, these panels, as utilized in the past, were not suitable for use in a clean-room environment because:
(1) the fibrous material present on the surface of conventional acoustical panels would break down in time and the surface-exposed fibers would be dislodged and free to move throughout the clean-room facility, thus creating a source of contamination; PA1 (2) washing or otherwise attempting to clean the panels would damage the surfaces thereof; and PA1 (3) repeated painting of the panels to maintain their appearance would destroy their sound absorbing capabilities, as well as necessitating labor-intensive operations which are, of course, time-consuming.
In later acoustical panel designs, such as that shown in U.S. Pat. No. 2,802,764, attempts were made to overcome the above-described problems by stretching a thin film or membrane of a material such as "Mylar" or "Saran" over exposed portions of the panel. Adding such a thin film, however, often caused the panel to warp and lose its desired predetermined shape. Normally, conventional acoustical panels have been in the form of rectangular parallelepipeds. Further, the film covering was simply not sufficiently durable to permit extended use and scrubbing in a manufacturing facility. Attempts by others to improve durability were too costly to be efficient.